Swimming may strengthen postmenopausal spines, if you do enough of it

Osteoporosis is a chronic disease that seriously affects health and quality of life, and it disproportionately affects women after menopause as bone mineral density declines. Exercise is a mainstay of bone health advice, but swimming occupies an awkward position in that conversation because the water supports the body's weight, leaving open the question of whether time in the pool does anything useful for the skeleton. This review set out to test exactly that: whether swimming affects bone mineral density at the spine and femoral neck in postmenopausal and premenopausal women with osteoporosis concerns.

Two investigators independently searched PubMed, Cochrane, EMBASE and EBSCO from inception to September 2019, using the keywords osteoporosis and swimming, with no language restrictions. From 256 relevant articles they screened down to five studies covering 263 participants, drawing on randomised controlled trial data comparing swimmers with nonswimmers. The main outcomes were bone mineral density and T-score, and lumbar spine density was reported in three of the included articles. The analysis also split swimmers into subgroups by swimming time: 3 to 6 hours versus under 3 hours.

Comparing swimmers with nonswimmers, lumbar spine bone density was improved in the swimmers, although the underlying studies showed a moderate level of disagreement with each other. The subgroup split proved decisive: bone mineral density was significantly higher than control in the 3 to 6 hour swimming group, while the under 3 hour group showed no effect at all. The authors note the benefit appeared especially in long-term swimmers. On the strength of this, they conclude swimming may improve bone density in postmenopausal women, while stating plainly that its effectiveness requires further investigation.

This finding complicates the common framing of swimming as irrelevant to bone because it is not weight-bearing, suggesting instead that volume and duration of swimming may matter. That said, the evidence base is genuinely small: five studies, 263 participants, and spine data from only three articles, with the trials in moderate disagreement. The review leaves open whether the effect holds at the femoral neck, how swimming compares with impact or resistance exercise for bone, and whether the time threshold is real or an artefact of which studies existed.

For swimmers, particularly postmenopausal women, this is a reason to think the pool may not be a dead loss for bone after all, and that the amount of swimming could be the variable that matters, since benefits appeared at 3 to 6 hours but not below 3. It is equally a reason for caution: with so few small studies, this is an early signal rather than an established effect, and the authors themselves call for more research. Anyone managing diagnosed osteoporosis is in territory where treatment decisions belong with their clinician.